Aims. We aim to characterize the multiwavelength emission from Markarian 501 (Mrk 501), quantify the energy-dependent variability, study the potential multiband correlations, and describe the temporal evolution of the broadband emission within leptonic theoretical scenarios. Methods. We organized a multiwavelength campaign to take place between March and July of 2012. Excellent temporal coverage was obtained with more than 25 instruments, including the MAGIC, FACT and VERITAS Cherenkov telescopes, the instruments on board the Swift and Fermi spacecraft, and the telescopes operated by the GASP-WEBT collaboration. Results. Mrk 501 showed a very high energy (VHE) gamma-ray flux above 0.2 TeV of similar to 0.5 times the Crab Nebula flux (CU) for most of the campaign. The highest activity occurred on 2012 June 9, when the VHE flux was similar to 3 CU, and the peak of the high-energy spectral component was found to be at similar to 2 TeV. Both the X-ray and VHE gamma-ray spectral slopes were measured to be extremely hard, with spectral indices <2 during most of the observing campaign, regardless of the X-ray and VHE flux. This study reports the hardest Mrk 501 VHE spectra measured to date. The fractional variability was found to increase with energy, with the highest variability occurring at VHE. Using the complete data set, we found correlation between the X-ray and VHE bands; however, if the June 9 flare is excluded, the correlation disappears (significance <3 sigma) despite the existence of substantial variability in the X-ray and VHE bands throughout the campaign. Conclusions. The unprecedentedly hard X-ray and VHE spectra measured imply that their low- and high-energy components peaked above 5 keV and 0.5 TeV, respectively, during a large fraction of the observing campaign, and hence that Mrk 501 behaved like an extreme high-frequency-peaked blazar (EHBL) throughout the 2012 observing season. This suggests that being an EHBL may not be a permanent characteristic of a blazar, but rather a state which may change over time. The data set acquired shows that the broadband spectral energy distribution (SED) of Mrk 501, and its transient evolution, is very complex, requiring, within the framework of synchrotron self-Compton (SSC) models, various emission regions for a satisfactory description. Nevertheless the one-zone SSC scenario can successfully describe the segments of the SED where most energy is emitted, with a significant correlation between the electron energy density and the VHE gamma-ray activity, suggesting that most of the variability may be explained by the injection of high-energy electrons. The one-zone SSC scenario used reproduces the behavior seen between the measured X-ray and VHE gamma-ray fluxes, and predicts that the correlation becomes stronger with increasing energy of the X-rays.
Aus dem Inhalt dieser Ausage: BEITRÄGE: Anuschka Tischer: Der Wandel politischer Kommunikation im Kriegsfall: Formen, Inhalte und Funktionen von Kriegsbegründungen der Kaiser Maximilian I. und Karl V., Mikko Huhtamies: Die schwedischen Militärkolonien im Baltikum während der so genannten schwedischen Großmachtperiode (1620-1720) – unter besonderer Berücksichtigung von Axel Oxenstiernas Grafschaft Wolmar-Wenden in Livland, Frank Göse: Otto Christoph Freiherr von Sparr (1605-1668) – erster brandenburgisch-preußischer Generalfeldmarschall : Vorüberlegungen zu einer biographischen Studie, PROJEKTE: Claudia Schmitz: Bedeutung und Wandel militärischer Konzepte und Institutionen im Verlauf der inkaischen Staatsentwicklung, Jan Willem Huntebrinker: „Fromme Knechte“ und „Garteteufel“. Die Konstruktion von Norm und Devianz bei Söldnern im 16. und 17. Jahrhundert, Heinrich Lang: Cosimo de’ Medici (1389-1464) und seine condottieri. Zur Außenpolitik der Republik Florenz im 15. Jahrhundert, Jens Warburg: „Soldatische Subjekte im modernen Krieg“, Roland Sennewald: Das Kursächsische Heer im Dreißigjährigen Krieg, BERICHTE: Hansjörg Buss: „Banal Militarism“ 15. und 16. Oktober 2004 in Marburg, Gundula Bavendamm: „The Revolutionary and Napoleonic Wars: New Approaches and Future Questions of Research“; Workshop am 1. November 2004 im Militärgeschichtlichen Forschungsamt Potsdam (MGFA), Michael J. Toennissen: „Militärische Helden – Helden im Krieg“ Jahrestagung des Arbeitskreises Militärgeschichte e. V. (AKM) vom 10. und 11. Dezember 2004 im Filmuseum Düsseldorf, REZENSIONEN: Frank Göse: Bernhard Mundt, Prinz Heinrich von Preußen 1726-1802 : die Entwicklung zur politischen und militärischen Führungspersönlichkeit(1726-1763), Hamburg 2002, Andrea Pühringer: Horst Carl, Hans-Henning Kortüm, Dieter Langewiesche, Friedrich Lenger (Hrsg.), Kriegsniederlagen : Erfahrungen und Erinnerungen, Akademie Verlag, Berlin 2004, ANKÜNDIGUNGEN: Die Rückkehr der Condottieri? Krieg und Militär im Spannungsfeld zwischen Verstaatlichung und Privatisierung. Die Entwicklung vom 16. Jahrhundert bis zur Gegenwart, 12. - 14. Mai 2006 in Potsdam